YI 2.5 Direct Measurement of Stiffness Index β of Superficial Arteries Without Blood Pressure Estimation

Background: Arterial stiffness index (β) is a clinically accepted vascular metric, calculated from arterial pressure and diameter obtained simultaneously from a single arterial site [1]. Hence, accurate measurement of β can only be performed on arteries where pressure can be recorded along with the diameter. We present a method to evaluate β from superficial arteries using arterial force (F) and diameter (D) waveforms, employing mathematical models (shown below) exploiting the non-linear pressure-diameter relationship [2], without requiring absolute pressure. Methods: Pilot functionality assessment was performed on eight participants (24 ± 5 years). A custom-developed frequency-matched system, combining single-element ultrasound and force-sensing transducers, was used to measure D and F waveforms from the common carotid artery. A hemodynamic-loop was formed from these measures and optimised to eliminate viscous components, and evaluate the elastic stiffness index β. Traditional β-formula [2] yielded reference values for comparison. fe(t)=fmx×(eβ(D(t)Dd−1)−1eβ(DsDd−1)−1) fe(t): Viscosity eliminated arterial force fmx: Maxima of viscosity eliminated arterial force β : Stiffness index D(t): Arterial diameter Ds: Systolic diameter Dd: Diastolic diameter Results: The system captured high fidelity D and F waveforms, adequate for reliable β evaluation. Measured group-average β (4.7 ± 0.8) was concurrent with literature. The measured β values statistically agreed (LoA = ±0.83 and bias = –0.32; non-significant p > 0.05) and strongly correlated (r = 0.93, p < 0.001) with the reference values. Further, they exhibited acceptable beat-to-beat repeatability (variation